Tunable and switchable all-fiber dual-wavelength mode locked laser based on Lyot filtering effect.

Mode-locked fiber lasers that generate two frequency combs with different frequency intervals could find very important applications in low-complexity dual-comb metrology. We report a partially polarization-maintaining all-fiber dual-wavelength dual-comb mode locked laser. The polarization dependent loss of the wavelength division multiplexer combined with the polarization-maintaining fibers leads to the periodic Lyot filtering effect. Traditional single wavelength mode locking can be realized with the tunable central wavelength and spectral shape. By properly setting the state of the polarization controller, stable dual-wavelength asynchronized mode locked pulse trains with the repetition rate difference of hundreds of Hertz can be achieved. In this dual-wavelength mode locked fiber laser, the dispersion of the laser cavity leads to group velocity difference of the two mode locked pulse trains with different central wavelengths, which results in the generation of dual-comb output with the frequency difference of hundreds of Hertz. The central wavelengths of the dual-wavelength mode locked fiber laser are demonstrated to be tunable in a certain range as well. Meanwhile, a novel dual-wavelength soliton molecule mode locking is also demonstrated. Such compact all-fiber dual-wavelength dual-comb mode locked laser could find various practical applications that in need of dual-comb fiber laser system.